1. Field of the Invention
The disclosure relates generally to an active element (an active structure controller, active vibration controller, active damping controller or active stiffness component, more particularly to a dynamic three-degree-of-freedom (3DOF) actuator/transducer element hereinafter called “Active 3D.O.F.” Stiffness Element (A3DSE) and, more particularly, to a mechanical design of an A3DSE and design issues related to the hardware involved in the A3DSE. In one embodiment, the A3DSE active element involves sensor and actuator components, mechanical interfaces between the active element and the machine and the assembly process and connection mechanisms. A specific embodiment is a dynamic three-degree-of-freedom actuator/transducer element (combined actuator and transducer element) comprising at least three piezoceramic actuators and force sensors, which are preloaded in the housing by a low-stiffness tension bar, and are constrained, by means of a flexible shell, against shear force and torsion moment, whereby the actuator/transducer element, when powered by an external voltage source, is able to generate a dynamical axial force and displacement and dynamical bending and moment in the two principal tilt degrees of freedom around two orthogonal axes perpendicular to the principal displacement, and when subjected to an axial force or a tilting moment, the transducer is able to generate charges that are proportional to the exerted force and moments.
2. Description of Related Art
Vibration control can be split up into passive and active methods. Passive vibration control methods directly deal with the physical properties of a machine, like its stiffness, mass and damping. Passive vibration control may boil down to a basic structural change, to the use of other materials, or simply to the addition of a “passive” element, i.e., an element the function of which does not need an external power source.
Active vibration control methods, on the other hand, depend on the use of an external power source. Active control traditionally belongs to the field of the control engineer. It is based on the use of sensors, actuators, signal conditioning electronics and control electronics, cooperating such that possible errors that may occur within a machine are anticipated or compensated for (Preumont 2002).